Solid wastes such as boiler fly ash, auto shredder residue ash, sewage sludge ash, and municipal solid waste incinerator ash account for a major portion of all solid wastes being landfilled in the U.S., and are therefore becoming a major environmental issue. These solid wastes contain heavy metal contaminants which require proper disposal methods to prevent leaching of the heavy metal contaminants into water supplies. This has focused attention on reducing landfilling and on regulations that prevent leachable toxic materials from being disposed of in landfills. Substantial efforts have, therefore, been made to develop uses for these solid waste materials as safe recycled products. Most of the past fly ash utilization efforts have been directed toward high volume usage applications with minimal processing requirements, such as fills, landfill cover, soil stabilization, and highway base courses. These efforts, however, have not adequately prevented the heavy metal contaminants from leaching into the environment.
Attempts have also been made to utilize fly ash in the production of cement, concrete, or other construction materials. U.S. Pat. No. 4,758,538 to Satoh, et al. discloses a process used to produce a foam ceramic body suitable as a building material by mixing various ceramic-forming materials with a blowing agent and heating the resulting mixture to 800.degree. to 1000.degree. C. at which temperature the mixture melts and softens. A clay or fly ash may be added to the mixture. The foam ceramic body is produced by forming the softened mixture into the desired shape, and then gradually cooling.
U.S. Pat. No. 5,346,549 to Johnson discloses a method of producing blocks or slabs from a mixture of fly ash and papermill waste. The fly ash, papermill waste, and a metal binding composite or heavy metal sequestering agent, are mixed together along with an oxidizer, fed on to a conveyor in a 1" thick layer, and exposed to electromagnetic energy, such as ultraviolet radiation, to soften the mixture and facilitate an oxidation reaction. The material can then be fabricated into products and dried at room temperature.
U.S. Pat. No. 5,366,548 to Riddle discloses a process of forming construction blocks which can encapsulate hazardous materials. Fly ash, bottom ash, water, additives, and hazardous material (if desired), are blended together to form a mixture which is then compressed under high pressure to form a fly ash body which is suitable for use as a construction material.
U.S. Pat. No. 4,112,033 to Lingl discloses a method of producing a brick or other ceramic product by mixing sewage sludge with clay, drying the mixture, and firing the dried mixture in a conventional kiln to oxidize the organic portions contained in the sludge into the bricks. Toxic exhaust gases, which are released during the mixing and drying stages, are vented to the kiln to undergo oxidation.
U.S. Pat. No. 5,273,566 to Balcar, et al. discloses a process of manufacturing glass abrasive particles by mixing waste materials comprising aluminum oxide and heavy metals (such as emission control dust or fly ash) with glass forming materials, heating the mixture in an oxidizing environment to oxidize the organic compounds and heavy metals so that the heavy metal oxides are vaporized and exhausted to a scrubber, and melting the remaining mixture to form a glasseous substance, which is quenched to form an abrasive material.
Although these procedures have been found to be useful in converting fly ash to a form useful as an end product, they do not sufficiently oxidize the organic materials and the metallic contaminants in the fly ash to produce a glass-ceramic product of uniform quality. Further, none of these procedures produce a high-value end product with significant market demand. As a result, economic justification for the capital and operational costs of implementing such procedures for disposal of fly ash tend to be problematic. The present invention is directed to overcoming these deficiencies.